1. Field of the Invention
This invention relates to an electrode and a process for the use thereof as an anode to oxidize either or both vanadium and uranium without deterioration of the anode and without oxygen generation at the anode.
2. Description of the Prior Art
Wet process phosphoric acid has been found to be a valuable source of vanadium and uranium. Numerous solvent extraction techniques have been developed to separate and recover the vanadium and uranium from the wet process phosphoric acid. The solvents employed in these various techniques normally are highly selective organic extractants which exhibit a particular affinity for either or both vanadium and uranium specie in a particular valence state. Vanadium and uranium normally are present in wet process phosphoric acid in the trivalent and quadrivalent oxidation states, respectively. In most processes, it is necessary to oxidize the vanadium and uranium to higher valence states to obtain effective solvent extraction. In many processes, the oxidation is effected through the addition of certain oxidants such as, for example, sodium chlorate, manganese dioxide, ozone and the like. The oxidant is added in an amount sufficient to provide at least the stoichiometric amount required for oxidation of all the vanadium and uranium. When the uranium and vanadium-free wet process phosphoric acid is to be used for animal feed supplements and the like, it is undesirable to add chemicals such as oxidants to the wet process phosphoric acid which will constitute a contaminant of the final end product.
Electrochemical oxidation of the vanadium and uranium can be effected through constant applied current and constant applied voltage techniques. A control system employing constant applied current maintains the current density constant regardless of the resistence changes in the load on the system. A control system employing constant applied voltage maintains the cell voltage of the system at a constant pre-determined voltage regardless of the percentage of load on the system.
All electrochemical reactions proceed to a specific end product by means of an electrical potential. The more closely this potential is maintained, the more efficient is the reaction. If the critical potential of an electrochemical reaction is maintained correctly, the current density and cell voltage can vary autonomously over a substantial range without adversely effecting the reaction.